ThreadUtil.sleep(interval); // 10 sec (default)
                    }

                    systemHelper.calibrateCpuLoad();
                    systemHelper.waitForNoWaitingThreads();

                    intervalControlHelper.delayByRules();

                    if (logger.isDebugEnabled()) {
                        logger.debug("Processing documents in IndexUpdater queue.");

        } finally {
            waitingThreadNames.remove(threadName);
        }
        return true;
    }

    /**
     * Waits for all waiting threads to complete.
     */
    public void waitForNoWaitingThreads() {
        int count = waitingThreadNames.size();
        while (count > 0) {
            if (logger.isInfoEnabled()) {
                logger.info("{} waiting thread(s).", count);
            }